In modern technology, it is frequently necessary or desirable to monitor various operating conditions for industrial processes and to retain a record of this information which can be analyzed or compared if the need should arise. For this purpose, various recording devices adapted to inscribe a visible curve on a record medium, such as an elongated strip chart, a circular chart or the like, driven at a given rate of speed so that variations in the monitored condition as a function of time are recorded in visible form have been developed.
With increasing emphasis being placed on the operation of industrial processes by remote control with a maximum of automation, it has become necessary to transmit the operating parameters for the given processes to remote locations, and curve scanning and transmitting systems, which will be referred to here as a "curve line reader", have been developed for this purpose. Such a system typically utilizes a television camera tube on the face of which is projected an optical image of a given portion of the recording medium to be read, and this optical image is repeatedly scanned by the electron beam of the camera tube at the usual high scanning rate along a substantially linear locus, extending at right angles to the length of the medium to be scanned. Since the optical density of the visible curve line differs from the background density of the medium, a pulse will be created in the video signal each time the beam crosses the curve line. Thus, the video signal gives an electronic representation of the location of each precise segment of the curve scanned by the electronic beam and from these signals, the original curve can be recreated at a remote point or fed either as analog or digital values to an electronic computer serving to process the data as may be desired.
Since the thickness of the curve line being detected by the scanning system is quite small, and may be of low density or contrast compared to the background, the precise detection of the curve line by the scanning system becomes difficult especially for differentiation from the "noise" present in the system. This "noise" may occur in the electronic components constituting the system or it may take the form of accidental smudges or spots on the background of the record material itself which are likewise capable of being picked up by the scanning system.
The object of the present invention is to provide a curve reader system which is relatively free from the influence of extraneous noise and provides a positive precise indication of the position of the curve line being scanned.